The present disclosure relates generally to material handling systems, and is more particularly directed to merge subsystems which merge articles carried by a plurality of conveyor lines onto a conveyor in single file.
In material handling systems, it is well known to use a merge subsystem to merge a plurality of article feed conveyors into a single line to meet the requirements of a downstream subsystem, such as a sortation subsystem. In high-speed material handling systems, such merging is often accomplished by use of one of two merge modes, a zippering merge mode or a slug-building merge mode. In the zippering merge mode, individual articles are released from a plurality of feed conveyors such that the articles are timed to be interleaved, or zippered, together with other articles released from the feed conveyors into a single file, with the appropriate inter-article gap between the articles. The zippering merge mode may utilize inter-article gaps between articles of different lines to avoid interference issues related to the articles of the different lines. In the slug-building merge mode, articles are accumulated into groups on a plurality of feed conveyors, with appropriate, minimal inter-article gaps between the articles in respective groups. Such groups are typically referred to as “slugs” or “trains.” Articles may be delayed on a staging conveyor until the slug is completed (or accumulated), at which time the articles of the built slug are released as a group. The time required to build a slug may be referred to as “slug-building overhead.” The slugs are selectively released, timed to be interleaved with other slugs, with the appropriate inter-slug gap between the slugs.
The performance (i.e., throughput of articles) of merge subsystems utilizing these two types of merge modes may depend on many things, including the speed of the merge, article lengths, and the sequence and timing of the arrival of articles at a merge conveyor. Since the zippering merge mode does not build slugs but instead utilizes inter-article gaps between articles from different conveyors, the zippering merge mode typically can deliver higher performance for a few input lines (e.g., approximately three to five input feed conveyors). As the number of input lines (e.g., feed conveyors) increases, the zippering merge mode performance reaches a maximum and may not increase with the addition of more input lines. In contrast, the slug-building merge mode takes time to build slugs and experiences “slug-building overhead,” making the slug-building merge mode less effective than the zippering merge mode when there are only a few input lines. However, once the number of input lines is large enough, the slug-building overhead is overcome and performance may be higher than the zippering merge mode.
During the design phase of a material handling system, a choice between the two merge configurations is typically made. Thus, from the design phase, typical material handling systems are either zipper merge systems or slug merge systems. Even when one of the two merge configurations is a clear choice for a given material handling system, there may be system conditions during operation of the material handling system that would be better handled by a different merge strategy than the one chosen.